A narrator begins the film by saying, "In this great city of Glasgow, there is a square which has nothing remarkable about its appearance; but there is one house that is exceptional: number seven. This house, which still remains, was the home of Madeleine Smith; perhaps her spirit still remains there, to listen for the tap of Emile LAngier's cane at her window. . ." The setting shifts from present day Glasgow to that same house in the year 1857 when Madeleine Smith, a young Scots-woman, lived there with her family. The daughter of a very prosperous and Victorian Glasgow merchant, Madeleine was bored with the proper and stodgy existence she led. At night, in the basement of her home, she would secretly meet her lover, Emile LAngier, a young, not-too-scrupulous Frenchman too poor to be formally presented to her stuffy Victorian family as a desirable catch. Meanwhile, Madeleine's father is increasingly annoyed at her continued refusal to marry Mr. Minnoch, a gentleman of her own breed. Just to keep her stem father happy, Madeleine becomes formally engaged to this affluent Scotsman.
Emile soon becomes jealous and threatens to show Madeleine's letters to her father if she won't introduce him to her family. Madeleine pleads with him to take her away so that they might be married and live else-where, but Emile refuses. Soon after Emile threatens to expose her as his mistress, he dies of arsenic poisoning. The letters come to light, and Madeleine is arrested and charged with murder.
She is brought to trial. The evidence is strongly against her, especially since she is known to have bought arsenic on several occasions. Yet, the defense points out that on the one occasion when she might have poisoned Emile, Madeleine also partook of the same chocolate served to him, which was brewed in the kitchen by the maid. Besides this, it is a number of weeks after this occasion that Emile dies.
As only a Scottish jury can do, the verdict is returned "case not proven." "That verdict," the narrator states, "means that Madeleine Smith left the court neither guilty nor not guilty, because the charge was 'not proven'," He continues, "Madeleine Smith, you have heard the indictment: were you guilty or not guflty?" As Madeleine Smith leaves the courthouse, driving off in a carriage, she looks into the camera and smiles.